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Rev Bras Med Esporte _ Vol. 13, Nº 5 – Set / Out, 2007 1. Programa de Pós-graduação em Educação Física, Universidade GamaFilho, Rio de Janeiro, RJ.
2. Curso de Educação Física, Universidade Estácio de Sá, Rio de Janeiro, RJ.
3. Department of Occupational Therapy, Faculty of Rehabilitation Medici-ne, University of Alberta, Edmonton, Alberta, Canadá.
Approved in 7/10/06.
Correspondence to: Paulo Sergio Chagas Gomes, Ph.D., Universidade Gama Filho, Programa de Pós-graduação em Educação Física – PPGEF, Rua Manoel Vitorino, 625, Piedade – 20748-900 – Rio de Janeiro, RJ, Brazil. Telefax: (21) 2599-7138. E-mail: crossbridges@ugf.br
Maximum number of repetitions in isotonic exercises:
influence of load, speed and rest interval between sets
Marta Inez Rodrigues Pereira1,2, Paulo Sergio Chagas Gomes1 and Yagesh Bhambhani3
O
RIGINALA
RTICLEKeywords: Intensity. Knee extension. Performance. Fatigue. ENGLISH VERSION
ABSTRACT
Introduction: Very little is known about the effects of move-ment velocity and rest intervals between sets of resistance exerci-se. Purpose: To compare the maximum number of repetitions to volitional fatigue (REPS) on a knee extension machine with the dominant leg for different loads, velocities and rest intervals be-tween sets. Methods: Nine volunteers (35.8 ± 10.8 years; 74.2 ± 16.7 kg; 171.0 ± 10.0 cm) reported to the laboratory to determine 1RM and REPS under six conditions, randomly determined and separated by at least 48 h: 1 set with 60% 1RM at 80°•s-1 and
25°•s-1; 1 set with 80% 1RM at 25°•s-1; 3 sets with 80% 1RM at
80°•s-1 and rest intervals of 3 min, 1 min and one that allowed
reco-very or stabilization of muscle oxygenation (RMox), measured by near infrared spectroscopy (NIRS). Results: Dependent samples t-test showed that REPS was significantly (p < 0.05) larger for the lighter than the heavier load, for slow (light = 8.8 ± 1.3; heavy = 5.9 ± 0.9) and fast velocities (light = 16.3 ± 3.9; heavy = 9.4 ± 1.9), and significantly larger for the fast than the slow velocity, for both loads. The 3x3 ANOVA did not show differences among intervals on set 1 (3 min = 9.4 ± 1.9; 1 min = 10.8 ± 3.2; RMox = 10.1 ± 3.0), however, there were significant differences on sets 2 and 3 be-tween 3 min (set 2 = 7.0 ± 1.7; set 3 = 6.4 ± 1.3) and 1 min (set 2 = 5.6 ± 1.1; set 3 = 4.8 ± 1.2), but not between RMox (set 2 = 6.4 ± 1.7; set 3 = 6.1 ± 1.5) and the other intervals. For all three inter-vals, REPS on set 1 was significantly larger than on the other sets.
Conclusions: Performance in resistance exercise is affected by load, velocity and rest interval between sets and is independent of muscle oxygenation recovery. Exercise prescription and assess-ment of performance should take these variables into consider-ation in view of the specific aims.
INTRODUCTION
Tests of maximum number of repetitions until volitional fatigue are commonly used in the exercise sciences field. Lighter loads result in more repetitions, although the exact number may vary according to the exercise being performed. Hoeger et al.(1)
com-pared the maximum number of repetitions with 40%, 60% and 80% of one maximum repetition (1 RM) in seven different upper and lower body exercises. Significant differences were observed in the number of repetitions among the exercises for the same % of 1 RM both for untrained and trained males as well as females.
The findings also showed significant differences between males and females, and trained and untrained.
Less evident in the literature is the fact that, lifting the same load, more repetitions will be performed with slower than faster movement speeds. The paucity of evidence in this respect is most probably due to the fact that most velocity-related studies are con-ducted with isokinetic dynamometers, where speed is controlled, but resistance and the applied force will vary. It is clear, though, that speed influences performance. Presently, the only evidence that velocity of movement influences performance during resis-tance exercises is reported in a study using push-ups and pull-ups(2)
and in studies from our own laboratory using squatting and chest press exercises(3-4).
Concerning the number of repetitions in multiple sets, again there are not many reports in the literature about isotonic exercises. The influence of between-sets rest intervals in performance has been mostly investigated with isokinetic dynamometers, and the results show that shorter intraset rest intervals are responsible for de-creases in performance of the subsequent sets(5-7). Studies from
our laboratory using isotonic bench press exercise have shown decreases in the number of repetitions in subsequent sets, and that shorter rest intervals (1 min) result in greater decreases than longer ones (2 or 3 min)(8-10). The physiological explanation for the
decrease in performance in multiple sets when, in theory, there is enough time for recovery of the energy substrates, is still not clear. It has been suggested that insufficient tissue oxygenation may be in some way related to fatigue. Moreover, there seems to be a dose-response correlation between force measured with electri-cal stimulation and muscle oxygenation(11) and a relation between
the rate of decrease in strength occurring with ischemia and oxy-gen availability, since this decrease was similar between the is-chemia and hypoxia conditions without blood flow interruption(12).
Therefore, it could be hypothesized that an intraset rest interval sufficient to recover muscle oxygenation would allow maintenance or smaller performance decrease of the sets following the first one.
Therefore, the purpose of this study was to compare the maxi-mum number of repetitions to volitional fatigue for unilateral leg extension using a conventional isotonic weight-lifting machine in the following situations: 1) different loads (60% and 80% 1 RM); 2) different speeds (25°•s-1 and 80°•s-1); 3) different rest intervals (1
min, 3 min and until stabilization of muscle oxygenation measured by near-infrared spectroscopy). The hypotheses tested were that there would be differences in the number of repetitions performed at different conditions, i.e.: 1) different percentages of 1 RM; 2) different movement speeds; 3) different recovery intervals.
METHODS
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participated in this study. All subjects have received verbal expla-nations of the study procedures and signed a written consent form prior to the beginning of testing. Study procedures were conduct-ed according to the institutional guidelines and the Helsinki Decla-ration.
Testing procedures
At least two days after the 1 RM load has been determined, subjects reported to the laboratory on six different days, separated by at least 48 h, when they performed the following tests of max-imum number of repetitions: 1) one set with 60% of 1 RM at 80°•s-1;
2) one set with 60% of 1 RM at 25°•s-1; 3) one set with 80% of 1
RM at 25°•s-1; 4) three sets with 80% of 1 RM at 80°•s-1 and 3 min
rest between sets; 5) three sets with 80% of 1 RM at 80°•s-1 and 1
min rest between sets; 6) three sets with 80% of 1 RM at 80°•s-1
and a rest interval between sets that allowed muscle oxygenation stabilization (RMox). Tests order was randomly determined. All test-ing was performed on a knee extension machine (Righetto Fitness Equipment, Campinas, SP, Brazil).
Muscle oxygenation recovery was determined by near-infrared spectroscopy (NIRS). NIRS is a non-invasive optical technique which determines relative oxy- and deoxy-hemoglobin blood concentra-tions through the different absorbance properties of these chro-mophores in the near-infrared spectrum (700 to 1000 nm). Detect-ed signal primarily originates, from the small circulation, representing the balance between supply and oxygen uptake in the monitored tissue. A two-wave length continuous NIRS device (MicroRunman, Philadelphia, PA, USA) has been used in this study, with the probe positioned over the dominant (as reported by the subject) vastus lateralis muscle, approximately 16 cm measured from the femur lateral epicondyle. Data obtained by NIRS repre-sent the phenomenon under the measured site, and detect, as in this case, what occurs in that specific region of one of the muscles strongly involved in the knee extension movement. The moment when the oxygenation curve (computed as subtraction of 760 nm and 850 nm signals(13)) stabilized was considered the muscle
oxy-genation recovery (figure 1).
One tester would control the extension angle and the other the movement cadence. The subject was verbally instructed to further extend the knee or speed up or down whenever he/she, in one repetition, did not attain the 70° minimum angle or was out of ca-dence, respectively. If the following repetition was still not within the breadth or rhythm set, the test was then ended. During the test, subject’s stabilization was attained by two testers, one hold-ing the subject’s hips against the seat, and the second immobiliz-ing the counter lateral leg.
Subjects first underwent a 10 repetitions warm-up using the cadence of the test to be performed with a load of approximately 40-50% of the test load. Seven minutes rest was allowed before the maximum test repetitions.
Data analysis
Paired t-tests have been used to compare the maximum num-ber of repetitions performed in the following tests: a) the single set at 60% of 1 RM and 80°•s-1 with the first set at 80% of 1 RM
and 80°•s-1, 3-min rest interval; b) the single set at 60% of 1 RM
and 25°•s-1 with the single set at 80% of 1 RM and 25°•s-1; c) the
single set at 60% of 1 RM and 25°•s-1 with the single set at 60% of
1 RM and 80°•s-1; d) the single set at 80% of 1 RM and 25°•s-1 with
the first set at 80% of 1 RM and 80°•s-1, 3-min rest interval. A 3x3
(sets x intervals) ANOVA for repeated measurements test was used to compare the maximum number of repetitions for the different rest intervals and sets. In case significance was found, post hoc analyses one-way ANOVA with repeated measurements tests were used, individually comparing each interval and each set. Differenc-es among intervals for the decrease in number of repetitions from the first to the last set were determined by a one-way ANOVA for repeated measurements. Significance level was established at p < 0.05.
RESULTS
The maximum number of repetitions performed in one set with different loads and speeds are shown in figure 2. Maximum repe-titions were significantly greater for the lighter than the heavier load, for both slow (p = 0.0001; light = 8.8 ± 1.3; heavy = 5.9 ± 0.9) and fast speeds (p = 0.0002; light = 16.3 ± 3.9; heavy = 9.4 ± 1.9) and significantly greater for the fast than the slow speed, for both lighter (p = 0.0001) and heavier loads (p = 0.0000).
The RMox interval ranged 1.6 ± 0.6 min, varying between 1.1 and 2.3 min, and was significantly (p < 0.01) different from the other two. Figure 3 shows the number of repetitions performed on the three sets of the three different rest intervals. Results of
Tempo (s)
Mox (D.O.)
Figure 1 – Graphic representation for a typical muscle oxygenation sub-ject during three sets of maximum repetitions of dominant knee exten-sion at 80% of 1 RM and 80°•s-1 with rest interval between sets sufficient
to stabilize muscle oxygenation (arrows indicate the moment of muscle oxygenation stabilization; black boxes represent contraction periods)
0 60 120 180 240 300 360 420 480 540 600 660 720
0,200
0,100
0,000
-0,100
-0,200
-0,300
-0,400
-0,500
Speeds were determined using a metronome set at 132 bpm. Slow speed used six beats for each phase of the movement, where-as fwhere-ast speed used two beats. The knee extension machine wwhere-as adapted so that range of motion could be monitored, and a repeti-tion was considered valid if the subject extended the knee to at least 70°, and not more than 90°. It resulted in average speeds per set varying from 25 to 29°•s-1 (average 26.6°•s-1) and 73 to 91°•s-1
(average 81.4°•s-1) for the slow and fast speeds, respectively.
Número de repetições
Figure 2 – Maximum repetitions (mean ± SD) in one set of unilateral knee extension with different movement speeds and different loads
* dependent samples t-test significantly (p < 0.05) greater than at 80% of 1RM for the same speed
† dependent samples t-test significantly (p < 0.05) greater than at 25°•s-1 for the same load
25
20
15
10
5
0
60% de 1 RM 80% de 1 RM
Velocidade Lenta (25o/s)
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Rev Bras Med Esporte _ Vol. 13, Nº 5 – Set / Out, 2007the 3x3 ANOVA indicated significant set x interval interaction (p = 0.0022) and set main effect (p = 0.0000). Subsequent analyses did not identify differences in number of repetitions among the first sets of each interval (3 min = 9.4 ± 1.9; 1 min = 10.8 ± 3.2; RMox = 10.1 ± 3.0); however, there were significant differences on the second and third sets between 3-min (set 2 = 7.0 ± 1.7; set 3 = 6.4 ± 1.3) and 1-min (set 2 = 5.6 ± 1.1; set 3 = 4.8 ± 1.2) intervals, with no differences between RMox (set 2 = 6.4 ± 1.7; set 3 = 6.1 ± 1.5) and 3-min or RMox and 1-min. For all three rest intervals, maxi-mum repetitions on the first set were significantly greater than those on the second (3-min, p = 0.0017; 1-min, p = 0.0003; RMox, p = 0.0127) and third sets (3-min, p = 0.0002; 1-min, p = 0.0005; RMox, p = 0.0041), with no differences between these two.
Considering the set main effect, differences were found in the total number of repetitions between set 1 (30.3 ± 7.4) and the other sets (set 2 = 19.0 ± 4.1, p = 0.0002; set 3 = 17.3 ± 3.2, p = 0.0004), with no differences between these two. Intervals main effect was not significant (p = 0.1844), indicating that the total number of repetitions in the three sets (3-min = 22.9 ± 4.5; 1-min = 21.1 ± 5.1; RMox = 22.7 ± 5.0) was not different among inter-vals. However, when the number of repetitions from the first to the last set was compared, using ANOVA for repeated measure-ments, significant difference was found among intervals (p = 0.0019), which was identified between the 1-min (6.0 ± 2.7) and the other intervals (3-min = 3.0 ± 1.2, p = 0.0056; RMox = 4.0 ± 2.5, p = 0.0053).
DISCUSSION
This study had the aim to compare performance measured as the maximum number of repetitions, with different intensities, dif-ferent speeds of movement, and difdif-ferent rest intervals between sets. The lighter load resulted in greater number of repetitions than the heavier one, and so did the faster speed when compared to the slower one. The intervals resulted in similar total number of repetitions; however, the shorter 1-min rest interval resulted in greater decreases in number of repetitions than the other inter-vals. When each set was individually compared, the longer rest interval (3-min) resulted in greater number of repetitions than 1-min (except for the first set). Nevertheless, muscle oxygenation recovery, with average duration of 1.6 min, did not result in a num-ber of repetitions different from the other two rest intervals.
The greater number of repetitions for the lighter load was ex-pected and agrees with the study by Hoeger et al.(1), in which the
lighter the load, the greater the number of repetitions achieved for
various exercises tested. In particular, for the knee extension exer-cise, these authors obtained between 13 and 18 repetitions at 60% of 1 RM approximately, and between 8 and 11 repetitions at 80% of 1 RM for both trained and untrained males and females. These outcomes are similar to those of the present study for the fast speed (approximately 16 repetitions at 60% of 1 RM and 9 repeti-tions at 80% of 1 RM), which is closer to that used when training this exercise with no movement speed control (86 ± 11°•s-1)(14).
It is well known that strength decreases with the increase of movement speed, which is referred to as the force-velocity rela-tionship. This relation is evident for isokinetic movements (when speed and resistance are externally controlled, whereas the exert-ed force is theoretically maximal throughout the entire range of motion)(15). The same is true for isotonic movement with
uncon-trolled movement speed; the greater the load, the slower the speed in which exercise is performed(16). When speed is voluntarily
con-trolled during isotonic exercise and then, the maximal load that can be lifted is observed, this relation seems to be inverted, and a greater load is possible to be lifted with faster speeds(4). According
to this reasoning, it is possible to perform more repetitions for a steady load, with faster speeds, compared to slower ones(2-3). The
explanation for this fact is not clear, but it is probably related to the fact that, with faster speeds, once inertia is overcome, the load’s momentum is greater and, thus, the force needed to be displaced may be reduced. In the present study, these findings were corrob-orated since, for both loads, the faster movement speed resulted in greater number of repetitions than the slower one.
This study’s results have previously confirmed research from our laboratory(8-10) which demonstrated that, in resistance exercise,
performance decreases in multiple sets, even with a 3-min rest interval. Moreover, performance with a 1-min rest interval is signif-icantly (p < 0.05) lower than with 3-min. Performance after muscle oxygenation recovery was not different from that with the other two rest intervals for each set, indicating that from approximately 1.5 min to 3 min, recovery seems to be equivalent and that, even though, fatigue affects performance. The decrease in number of repetitions for the 3-min and RMox intervals was greater than that reported by Kraemer et al.(17) for knee extension with a 2-min rest
interval between sets (set 1 = 9.5 ± 1.0; set 2 = 8.9 ± 2.0; set 3 = 7.9 ± 1.9). However, these authors used bilateral knee extensions and a speed of approximately 45°•s-1, which is slower than the
80°•s-1 of the present study. It is surprising the fact that values
reported by Kraemer et al.(17) are greater, since it would be
expect-ed that with a slower speexpect-ed the number of repetitions would be even smaller than with a faster one. Differences in results are prob-ably partly due to the fact that those authors used bilateral move-ment, whereas this study used only the dominant leg.
Results of this study show that muscle oxygenation level con-sidered as the moment when muscle oxygenation measured by NIRS stabilizes was not a determinant factor for activity perfor-mance. Studies by Murthy et al.(11) and Hogan et al.(12) that found
an association between decrease in strength and muscle oxygen-ation were performed with electrical stimuloxygen-ation, which may result in performance different from that obtained through in vivo volun-tary contraction.
In the present study, recovery for beginning of the next set was considered as stabilization of the oxygenation curve, not return to baseline levels. It is possible that this was not sufficient for com-plete recovery since none of the subject of this study showed sta-bilization at baseline levels (figure 1), even after three minutes of recovery. Thus, future studies should investigate whether recov-ery of muscle oxygenation to baseline levels is determinant to maintain performance levels. Furthermore, decrease in perfor-mance with shorter rest intervals may be related to factors other than muscle oxygenation, such as increase in blood lactate con-centration(18-19), related to increases in H+ which in turn, reduces
the force generating capacity(20).
Número de repetições
Figure 3 – Maximum repetitions (mean ± SD) in three sets of unilateral knee extensions at 80% of 1 RM and 80°•s-1, with different rest intervals
between sets
RMox – muscle oxygenation recovery
* repeated measures ANOVA significantly (p < 0.05) greater than the same set with 1-min interval † repeated measures ANOVA significantly (p < 0.05) greater than the other sets with the same
interval
16
14
12
10
8
6
4
2
0
3 min 1 min RMox
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Other studies have also reported differences in number of repe-titions between sets and rest intervals. On the bench press exer-cise(21), the number of repetitions on the second and last set was
significantly different among 1-min, 3-min and 5-min intervals, and smaller than that performed on the respective first sets. Hannie et al.(22) observed decreases in the number of repetitions in four sets
of bench press after 2-min of either passive or active (cycle ergom-eter) rest intervals. Recent unpublished data from our laboratory corroborated the decrease in number of repetitions in three sets of knee extension with a 3-min rest interval, after different intensi-ties of a specific warm-up routine. Surprisingly, Firmino et al.(23)
hardly showed any decrease in performance on the leg press and knee extension, with 2-min rest intervals between sets, after sub-jects had performed different warm-up routines (aerobic or specif-ic). It should be observed that on the second set of leg press after both warm-ups, the number of repetitions performed was exactly that which was expected (10RM) and the standard deviation was zero, indicating that all subjects performed the same number of repetitions.
It is possible that longer rest intervals between sets may allow better recovery. Willardson and Burkett(24), when comparing the
total number of repetitions performed in four sets with 1-min, 2-min and 5-2-min intervals, on the squat and bench press, observed that the 5-min rest interval resulted in a greater number of repeti-tions than the other two recovery intervals for both exercises; how-ever, for the squat, differences between 1-min and 2-min were not significant, whereas for the bench press, the 1-min rest resulted in a smaller total number of repetitions. Repetitions between sets were not statistically compared; nevertheless, decreases in mean values of 68 and 47% for the 1-min rest interval, of 49 and 40% for the 2-min, and 26 and 25% for the 5-min, for bench press and squat exercises, respectively, may be observed, suggesting that even five minutes may not be enough to maintain performance.
CONCLUSIONS
Performance in resistance exercise, measured as the maximum number of repetitions, is affected by load, speed of movement and rest interval between sets. Greater intentional movement speed allows greater number of maximum repetitions for a same load, no matter whether it is lighter (60% of 1 RM) or heavier (80% of 1 RM). Three-minute rest intervals between sets result in greater number of repetitions in multiple sets when compared to 1-min, although they are not sufficient to maintain the same performance of the first set. Similarly, stabilization of muscle oxygenation does not seem to be enough to maintain performance in multiple sets of resistance exercise. Further studies are needed to investigate whether complete muscle oxygenation recovery to baseline levels is necessary to allow better performance in multiple sets.
It is worth mentioning that NIRS technique is subject to limita-tions, including the fact that it detects oxygenation levels of an area underneath the site where the probe is positioned, and does not represent the whole muscle group responsible for knee exten-sion. It is possible that different oxygenation levels obtained from other parts of the muscle or from synergistic muscles could better explain the differences in number of repetitions between sets.
According to the outcomes of this study, exercise prescription and especially performance assessment, more so for research purposes, should take into account load, speed and rest interval between sets in order to obtain the desired objectives. As for train-ing, it is still early to say that using faster speeds in order to obtain greater number of repetitions is more efficient than slower speeds with a smaller number of repetitions, since an earlier study has demonstrated that training at 25o•s-1 and 100o•s-1 resulted in similar
gains in strength(25).
ACKNOWLEDGMENTS
This study was partly supported by CAPES/Ministry of Education, FEP-ERJ (E-26/170.774/2003), and Righetto Fitness Equipment, Brazil.
All the authors declared there is not any potential conflict of inter-ests regarding this article.
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